The Murine Gammaherpesvirus 68 ORF27 Gene Product Contributes to Intercellular Viral Spread

Abstract

Herpesviruses remain predominantly cell associated within their hosts, implying that they spread between cells by a mechanism distinct from free virion release. We previously identified the efficient release of murine gammaherpesvirus 68 (MHV-68) virions as a function of the viral gp150 protein. Here we show that the MHV-68 ORF27 gene product, gp48, contributes to the direct spread of viruses from lytically infected to uninfected cells. Monoclonal antibodies to gp48 identified it on infected cell surfaces and in virions. gp48-deficient viruses showed no obvious deficit in virion cell binding, single-cycle replication, or virion release but had reduced lytic propagation between cells. After intranasal infection of mice, ORF27-deficient viruses were impaired predominantly in lytic replication in the lungs. There was a small deficit in latency establishment, but long-term latency appeared normal. Since ORF27 has homologs in both Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, it is likely part of a conserved mechanism employed by gammaherpesviruses to disseminate lytically in their hosts.Epidemic viruses generally rely on high infectivities to transmit infection before immune responses become effective. In contrast, persistent viruses use immune evasion to establish a state of chronic, low-level infectivity. In keeping with this strategy of stealth, persistent viruses generally release virions only in very specific settings and otherwise spread via cell-cell contact.Herpesviruses are archetypal persistent pathogens. Acute infections are not associated with a detectable viremia, consistent with a predominance of direct, cell-to-cell virus transfer. In herpes simplex virus, this is a function of gE and gI, which are dispensable for lytic replication in vitro but contribute to dissemination in vivo (11). Glycoprotein D of pseudorabies virus, which binds virions to cells, illustrates the converse: it is important for growth in vitro but dispensable for growth in vivo (22). Thus, spread by virion release and spread by cell-cell contact, though clearly overlapping in their requirements for membrane fusion, appear to be separable processes involving distinct attachment proteins. Any therapeutic intervention must therefore encompass these two separate modes of viral spread.We are interested in the molecular processes that underlie the dissemination of gammaherpesviruses. These viruses lack genetic homologs of alphaherpesvirus gE and gI. The virusdriven proliferation of latently infected lymphocytes plays a central role in host colonization by gammaherpesviruses (8), but lytic replication must still be required for entry into and exit from hosts as well as for viral transit between different cell types. Cell-binding virion proteins have been identified for Epstein-Barr virus (EBV) (6, 32) and Kaposi's sarcoma-associated herpesvirus (KSHV) (2), but the processes by which gammaherpesviruses spread between cells in vivo remain unknown. Moreover, the strict species tropisms of EBV and KSHV make it difficult to u...

Proteomic Characterization of Bovine Herpesvirus 4 Extracellular Virions

“…However, in contrast with other rhadinoviruses, BoHV-4 does not encode any ORF4 or ORF74 homologues, and only four other potential envelope glycoproteins were predicted in the BoHV-4 genome: ORF27, ORF53, ORF58, and Bo9. The proteins encoded by ORF27 and ORF58 are involved in intercellular viral spread in MuHV-4 (35,36). One hypothesis could therefore be that different virions are produced following the major way of dissemination.…”

Epstein–Barr virus BDLF2–BMRF2 complex affects cellular morphology

“…The authors proposed that bdlf2 is a late gene in the EBV lytic cycle in epithelial cells. May et al (2005b) recently showed that ORF27, a distantly related BDLF2 homologue from murine herpesvirus 68 (MHV-68) is required for cell-to-cell spreading. However, the same authors revealed that ORF27 interacts with ORF58, the BMRF2 homologue, and this interaction influences their subcellular distribution (May et al, 2005b).…”

“…May et al (2005b) recently showed that ORF27, a distantly related BDLF2 homologue from murine herpesvirus 68 (MHV-68) is required for cell-to-cell spreading. However, the same authors revealed that ORF27 interacts with ORF58, the BMRF2 homologue, and this interaction influences their subcellular distribution (May et al, 2005b). It appears that the expression of ORF58 is sufficient to induce the export of ORF27 from the endoplasmic reticulum (ER) and transport of the noncovalent ORF58/ORF27 complex to the plasma membrane.…”

A Replication-Deficient Murine γ-Herpesvirus Blocked in Late Viral Gene Expression Can Establish Latency and Elicit Protective Cellular Immunity

“…Finally, Ab has effector functions other than neutralization. For example, it is likely that Ab plays a role in controlling viral spread and viral reactivation, as gp150 and gp48 have been shown to promote virion release and intercellular viral spread (57)(58)(59). Since both humoral and cellular immunity have been shown to be involved in controlling distinct stages of ␥-herpesvirus infection, and the importance of neutralizing Abs for viruses that spread mainly by cell-cell contact is unclear, we cannot conclude that the absence of neutralizing Abs following i.p.…”